The present invention relates to a passive, active or mixed platform type antenna orienting apparatus carried on a vehicle, such as a small-sized vessel or an automobile, which turns frequently and experiences complex vibrations, for tracing a target such as a communications satellite with a directive antenna. And more particularly, to an antenna orienting apparatus for a vehicle, which is freed from entanglements of a cable leading to the antenna due to circular travel of the vehicle, and which can provide isolation of the antenna from vehicular vibrations and using a light weight antenna and dampening system.
The orientation of a communications satellite or target is uniquely decided if its azimuth or elevation angle is determined. The azimuth is an angle which measures the orientation of the satellite clockwise from the north in a horizontal plane, and the elevation is an angle which is made between the satellite, the antenna, and the horizontal plane.
Moreover, these angles are functions of the present position of the vehicle, i.e., the longitude and the latitude. Thus, the vehicle is required to trace the satellite by computing the azimuth and elevation on the basis of the data of its present location. The apparatus carried on a vehicle for orienting the satellite communications antenna is ordinarily equipped with a tracing mechanism including a CPU and a servo mechanism. However, the antenna orienting apparatus must maintain an orientation directed to the communications satellite while the vehicle turns to provide satisfactory communication.
A north-directing gyro for computing the present location is provided along with a vertical gyro for giving a vertical reference. The orientation of the antenna can be maintained toward the communications satellite, if the vertical gyro is used to detect the turns or motions (e.g., a rolling or pitching angle in case of a vessel) of the vehicle and its signal drives the aforementioned servo mechanism. This method is of the active platform type, in which the antenna is stabilized together with its orientation control. In this active platform type antenna orienting apparatus, the motions of the antenna are compensated for those of the vehicle, so that the vehicle does not deteriorate the directivity when severe, as in a small-sized vessel.
In contrast to the active platform type, there is known a passive platform type antenna orienting apparatus for stabilizing the antenna by means of a gyro mechanism. This will be described with reference to FIG. 4. An antenna 1 is supported in a rocking manner by an elevation shaft 3 through an elevation panel 2. This elevation shaft 3 is borne in a stable platform 4, which is turnably supported by a shaft 9a. To this shaft 9a, there are attached through a turnable swivel cylinder 5 two flywheels 6 and 7 which have momentums in a vertical swivel axis.
The shaft 9a is connected through a universal joint 8 to a shaft 9b. This shaft 9b has its lower portions fitted in sliding holes 11 and 12 of a post 10. A bias spring 15 is mounted between a flange 3 of the shaft 9 and a partition 14 of the post 10. A shock absorbing action against the vertical or axial vibration is established by the friction between the sliding holes 11 and 12 and the shaft 9 and by the elastic force of the bias spring 15. The post 10 is supported through a spherical bearing 7 disposed at the center of a base 16, and bias springs 20, having a sliding case, are mounted between four arms 18 extending from the lower end of the post 10 and the folded extensions 19. A shock absorbing action against the horizontal vibration is established by the friction of the sliding case attached to the bias springs 20 and by the elastic force of the bias springs 20. Coupling the stable platform 4 and the shaft 9a, moreover there are gears 21 and an azimuth electric motor 22 to orient the antenna 1 to a predetermined azimuth angle. Between the stable platform 4 and the elevation shaft 3, there are disposed gears 23 and an elevation shaft electric motor 24, orient the antenna 1 to a predetermined elevation angle. Additionally: numeral 25 designates a controller attached to the stable platform 4; numeral 26 designates a power supply/control unit; and numeral 27 designates a vehicle such as a fishing boat or the like.
If the vehicle 27 makes either an abrupt turn, changing its direction or a rocking motion such as a rolling or pitching motion, the stable platform 4 of the antenna orienting apparatus thus constructed is always enabled to hold its position, for example, in a horizontal attitude by the bending structure of the universal joint 8 and by the inertial forces of the flywheels 6 and 7. The orientation control of the antenna 1 is carried out by the azimuth shaft motor 22 and the elevation shaft motor 24, as described above.
FIG. 5 is a control block schematic of the antenna orienting apparatus of FIG. 4. The rotary side includes the devices above the stable platform 4 of FIG. 4, and the stationary side includes the devices below the shaft 9a of FIG. 4. A power source/control unit 26, is connected through bendable cables 29a to 29e to a stable platform mechanism 28 for driving the flywheels, a power supply 29 for individual portions, a high power amplifier 25a for the controller 25, the elevation shaft motor 24, a position sensor 24a for the motor 24, the azimuth shaft motor 22, and a position sensor 22a for the motor 22. The controller 25 has its send signal TX/lF, receive signal RX/lF and local oscillator reference signal REF connected through bendable cables 30a to 30c with a coaxial cable 31.
A first defect of the antenna orienting apparatus thus constructed according to the prior art is that the rotary side and the stationary side are connected through the cables. If the vehicle continuously turns in one direction the cables 29a to 20e and 30a to 30c coil around the shafts 9a and 9b of FIG. 4 either to make it impossible to control the attitude or to disconnect the cables. Thus, a rotary limiter is provided to rewind the stable platform 4 when this platform 4 rotates to its limit, thereby to prevent the coiling of the cables. In order to effect the rewinding, the communications have to be interrupted. A second defect of the antenna orienting apparatus of the prior art resides in the construction that the horizontal vibration is damped by the bias springs 20 at the leading ends of the four arms 18. Especially in a small-sized vessel such as a fishing boat, the horizontal vibration is stronger than the vertical or axial vibration. The bending moment exerted by the bias springs upon the arms 18 tends to break these arms 18. Because of as few as four arms 18, moreover, the damping action is not uniform in the horizontal direction.
It is, therefore, an object of the present invention to provide an antenna orienting apparatus for a vehicle, which is freed from any coiling of cables so that the antenna can rotate many times without interruption of communications. Another object of the present invention is to provide an antenna orienting apparatus for a vehicle, which can dampen the horizontal vibration efficiently and make the weight of the portion to be damped, as light as possible.